In wireless communication systems, radio resource management (RRM) is responsible for utilization of the air interface resources. RRM is generally called upon for three reasons: to guarantee quality of service (QoS), to maintain the planned coverage area, and to offer high capacity. Call admission control (CAC) is a part of RRM. The CAC function accepts or rejects a request to establish a radio access bearer channel in the radio access network. The RRM CAC function is generally located in the controlling radio network controller (C-RNC), where the load information from several cells can be obtained.
In general, whenever a call is received, the RRM CAC function in the C-RNC will determine whether sufficient physical resources are available to meet the requirements of the call. If the resources are available, the CAC function will allocate the resources for the call; otherwise it will reject the request. Improper call admission decisions result in sub-optimal radio resource allocations. This can lead to unnecessary dropped calls or idle resources.
If the information needed during CAC was collected “on the fly,” there would be a processing delay imposed because the C-RNC would need to query several different entities to gather all of the information. Such a manner of collection would also add the risk that the required information is not available, causing either the failure of CAC or an unacceptably long delay in obtaining the information.